1. Technical Field
The present invention concerns a control system for operating electromagnetic pumps. More specifically, the invention relates to a control system and method in accordance with the claims.
2. Technical Background
Electromagnetic pumps that apply pressure or negative pressure are found in a large variety of variations and sizes and are used in many different applications, everything from large industrial pumps to very small pumps for medical purposes. The diverse areas of use for electromagnetic pumps such as membrane pumps results in a plethora of requirements put upon the performance of such pumps. A significant problem for buyers of membrane pumps is that the supply of pumps from manufacturers is to a large degree standardized to just a few different models, largely because pump manufacturers seek economies of scale in their production. The limited diversity of pumps means that there exists a need for more efficient control systems. This would allow manufacturers to satisfy specific user needs in a much better way and thereby reduce costs as well as improve the performance of products that contain a pump. Today there is a lack of good quality, simple, standardized, low maintenance and inexpensive control systems for electromagnetic pumps.
It is quite common that membrane pumps are driven with the aid of one or more electromagnets. An electromagnet produces a back and forth movement that for example causes the membrane to produce a pumping movement. An advantage with electromagnetic driven membrane pumps is that they are more closely coupled to the membrane which renders it possible for example to vary the length of stroke, which can not be accomplished by membrane pumps powered by rotating motors with an eccentric. Furthermore, electromagnetic pumps are comprised of very few details which make them inexpensive to manufacture. Electromagnetic pumps are still less common despite this because of several problems that result in the fact that an electromagnet is not obviously better at powering a membrane pump compared with a rotating motor. A significant problem with electromagnetic driven pumps is that they are difficult to gear up for higher pressure without introducing lever that entail more details and additional friction. Yet another problem is that it is difficult to optimize electromagnetic pumps to turn precisely at their closing position without hitting the bottom of the pump. Hitting the bottom results in a shorter life span and turning to early results in poorer pressure performance. Electromagnetic pumps are therefore often pre-set to a certain pressure that can not be changed, which in turn is often a problem because this results in significant limitations. Still another problem with electromagnetic pumps is that they are more complicated to control than pumps with a rotating motor and they often can only be controlled by the amount of voltage.
Additional problems that exist originate from the actual implementation and use of pumps. During the use of oscillating pumps such as electromagnetic pumps and pumps with rotating motors with eccentrics, oscillations are created in pressure and flow. These are in many cases unwanted and can for example disturb measuring sensors which measure the pumped medium. So called air capacitors, a large vessel or volume, are often used to even out the flow in order to minimize the disrupting oscillation. This is not however always a good solution because they take into use a lot of space and the pumped medium risks being mixed in these vessels before the medium finally reaches the gas sensor. This reduces for example the sensitivity and the response time of the measuring system. Another problem with the use of pumps is that flow is affected by how high the pressure is in the system. It is often desired that flow and pressure be constant. The performance of the pump depends a lot on if the surrounding pressure for some reason changes. This means that one must measure pressure or flow or both with good precision and in many applications this is necessary in order to control the pump. This increases the cost and complexity of the system. Yet another problem is when several pumps must be coordinated in order to attain a common result, such as the mixing of gases. This creates very complex systems with several flow meters, pressure meters and valves. It is also a problem to acquire a control system that is completely free from calibration and that is not affected by operation and aging.
Because of the above mentioned problems systems and products that include pumps often give rise to very intricate designs comprised of many details malting production very costly.